The objective of these studies is to describe in detail the interrelationships of neurons comprising the cerebral neocortex. We are studying the barrels in layer IV of the mouse SmI because they have been shown to have a consistent appearance and arrangement from specimen to specimen and are known to be related to the vibrissae on the contralateral face in a one-to-one manner. The studies are five-fold: (1) to characterize the neuronal population qualitatively and quantitatively in Golgi and EM preparations; (2) to establish the connections of the barrels using autoradiography and degeneration techniques; (3) to examine the development of the barrels with quantitative techniques in normal postnatal material and how this is modified by early damage to the vibrissae; (4) to study a variety of murine mutants; (5) to determine the prevalence and variation of the barrels in the mammalian kingdom using a comparative approach.